Autofocusing zoom lens

ABSTRACT

In an autofocusing zoom lens, a depth of focus ε is obtained based on an aperture value Fno of a variable diaphragm and a diameter of a permissible circle of confusion δ. A focal position variation amount Δsk for a predetermined positional displacement amount ΔFp 0  of a focusing lens unit is obtained according to a position Fp of the focusing lens unit and a variable magnification state Zp. If a predetermined variation amount ΔFp of the focusing lens unit satisfies a first condition, the focusing lens unit is not driven. If the first condition is not satisfied and a second condition is satisfied, the focusing lens unit is driven based on a second autofocusing unit, and if the second condition is not satisfied, the focusing lens unit is driven based on a first autofocusing unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application pursuant to 37 CFR §1.53(b)of prior U.S. application Ser. No. 13/075,669 filed Mar. 30, 2011 whichclaims foreign priority benefit from Japanese Patent Application No.2010-081437 filed Mar. 31, 2010, the disclosures of which are herebyincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an autofocusing zoom lens whichincludes a distance measurement unit provided separately from aphotographic optical system and configured to execute focusing.

2. Description of the Related Art

In recent years, a broadcast high-definition (HD) recording system hasbeen widely used and a large-size home monitor has been used. Underthese circumstances, sufficient focusing accuracy cannot be achieved bymerely executing manual focusing as in a conventional method.Accordingly, a problem of a defocused image often occurs. To solve theabove-described problem, it is desired that a lens for an HD system havea highly accurate autofocusing function.

As an autofocusing method, a contrast autofocusing method, which uses avideo signal from an imaging unit, such as a charge-coupled device (CCD)sensor, is widely known. In addition, an external light autofocusingmethod, which uses a distance measurement unit that executes atrigonometric distance measurement operation, is also widely known.

For example, Japanese Patent No. 3738795 discusses a method that usesthe contrast autofocusing method and the external autofocusing methoddescribed above in combination. More specifically, the conventionalmethod switches the autofocusing methods according to variousconditions, such as the temperature inside or outside the apparatus, anaperture value, or a focal length.

The zoom lens discussed in Japanese Patent No. 3738795 is a rear-focustype zoom lens capable of executing focusing with a high accuracy by thecontrast autofocusing method after roughly executing focusing by theexternal autofocusing method. With this configuration, the zoom lensdiscussed in Japanese Patent No. 3738795 can achieve quick and highlyaccurate focusing.

However, in the broadcasting industry, in which a user is particularabout shooting a normal image, the user is interested in the normalityof the image rather than the speed of focusing.

In the contrast autofocusing method, an operation for focusing isnecessary in calculating a maximum value of contrast. Therefore, anabnormality of a video, such as overshooting or vibrated reproduction ofa defocused image, may occur. Accordingly, it is desired that thecontrast autofocusing method be used under restricted conditions of use.

SUMMARY OF THE INVENTION

The present invention is directed to an autofocusing zoom lens capableof executing a focusing operation at a high speed, with a high accuracy,and with no abnormality occurring on an image obtained by executingappropriate control of focus driving according to states of zooming,focusing, and an aperture.

According to an aspect of the present invention, an autofocusing zoomlens, which is capable of being detachably mounted on an image pickupapparatus and includes, in order from an object side to an image side, afocusing lens unit configured to move during focusing, avariable-magnification lens unit configured to move during variation ofmagnification, and a variable diaphragm capable of varying an aperturediameter, includes a position detection unit configured to detect aposition of the focusing lens unit, a magnification-varying statedetection unit configured to detect a position of thevariable-magnification lens unit, and an aperture value detection unitconfigured to detect an aperture value of the variable diaphragm, adistance measurement unit configured to measure a distance to an object,a communication unit configured to communicate with the image pickupapparatus, a video signal receiving unit configured to receive a videosignal from the image pickup apparatus, a first autofocusing unitconfigured to drive the focusing lens unit based on a result ofdetection by the distance measurement unit, and a second autofocusingunit configured to drive the focusing lens unit based on the videosignal from the image pickup apparatus. In the autofocusing zoom lens, adepth of focus ε is obtained based on an aperture value Fno of thevariable diaphragm and a diameter of a permissible circle of confusionδ. A focal position variation amount Δsk for a predetermined positionaldisplacement amount ΔFp0 of the focusing lens unit is obtained accordingto a position Fp of the focusing lens unit and a variable magnificationstate Zp. If a predetermined variation amount ΔFp of the focusing lensunit satisfies the following first condition:|ΔFp·Δsk|−ε≦0,the focusing lens unit is not driven. If the first condition is notsatisfied and the following second condition is satisfied:|Δsk|−ε>0 andΔFp0−|ΔFp|>0,the focusing lens unit is driven based on the second autofocusing unit,and if the second condition is not satisfied, the focusing lens unit isdriven based on the first autofocusing unit.

According to another aspect of the present invention, an autofocusingzoom lens, which is capable of being detachably mounted on an imagepickup apparatus and includes, in order from an object side to an imageside, a focusing lens unit configured to move during focusing, avariable-magnification lens unit configured to move during variation ofmagnification, and a variable diaphragm capable of varying an aperturediameter, includes a position detection unit configured to detect aposition of the focusing lens unit, a magnification-varying statedetection unit configured to detect a position of thevariable-magnification lens unit, and an aperture value detection unitconfigured to detect an aperture value of the variable diaphragm, adistance measurement unit configured to measure a distance to an object,a communication unit configured to communicate with the image pickupapparatus, a video signal receiving unit configured to receive a videosignal from the image pickup apparatus, a first autofocusing unitconfigured to drive the focusing lens unit based on a result ofdetection by the distance measurement unit, and a second autofocusingunit configured to drive the focusing lens unit based on the videosignal from the image pickup apparatus. In the autofocusing zoom lens, anear point distance Sn and a far point distance Sf are obtained based ona focal length F and a diameter of a permissible circle of confusion δ.If a current focus position Obj and a resolution Det of the distancemeasurement unit satisfy the following first condition:Sf−Obj>0 orObj−Sn>0,the focusing lens unit is not driven. If the first condition is notsatisfied and the following second condition is satisfied:(Sf−Sn)−Det<0 andSf−Obj <0 orObj−Sn<0,the focusing lens unit is driven based on the second autofocusing unit,and if the second condition is not satisfied, the focusing lens unit isdriven based on the first autofocusing unit.

According to yet another aspect of the present invention, a cameraapparatus includes the autofocusing zoom lens, and an image pickupapparatus (image sensor) located on the image side of the autofocusingzoom lens.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the present invention.

FIG. 1 illustrates an exemplary configuration of an image pickupapparatus having a zoom lens according to a first exemplary embodimentof the present invention.

FIG. 2 illustrates the principle of a distance measurement unit.

FIG. 3 illustrates an exemplary method of forming an image by a focusinglens unit, which is provided to a zoom lens at a location closest to theobject side.

FIG. 4 illustrates an exemplary correlation between a position of adistance measurement sensor of a distance measurement unit and aposition of the focusing lens unit.

FIG. 5 is a table storing data of an amount of variation of focalposition in relation to an amount of variation of the focusing lensunit.

FIG. 6 is a flow chart illustrating an exemplary flow of an autofocusingoperation according to the first exemplary embodiment.

FIG. 7 illustrates an exemplary configuration of an image pickupapparatus having a zoom lens according to a second exemplary embodimentof the present invention.

FIG. 8 is a flow chart illustrating an exemplary flow of processingaccording to the second exemplary embodiment.

FIG. 9 illustrates an exemplary configuration of an image pickupapparatus having a zoom lens according to a third exemplary embodimentof the present invention.

FIG. 10 is a flow chart illustrating an exemplary flow of processingaccording to the third exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

FIG. 1 illustrates an exemplary configuration of an autofocusing zoomlens and an image pickup apparatus according to a first exemplaryembodiment of the present invention. Referring to FIG. 1, a cameraapparatus is constituted by an image pickup apparatus 200 and anautofocusing zoom lens 100. The zoom lens 100 is detachably mounted onthe image pickup apparatus 200, so that it can be interchanged withother zoom lens.

The zoom lens 100 includes a focusing lens unit 1, avariable-magnification lens unit 2, a variable diaphragm 3, and anextender lens unit 4. The focusing lens unit 1 is stationary duringvariation of magnification along an optical axis. Thevariable-magnification lens unit 2 includes a plurality of lenses andhas a variable magnification (magnification-varying) function. Thefocusing lens unit 1, the variable-magnification lens unit 2 and thevariable diaphragm 3 are disposed along the optical axis of the zoomlens 100, while the extender lens unit 4 enters into and exits from theoptical axis to change the focal length of the zoom lens 100. Thefocusing lens unit 1 is driven by a focus motor 5 under control of thefocus control unit 25.

A detection unit 11 detects a position of the focusing lens unit 1. Adetection unit 12 detects a state of variable magnification by thevariable-magnification lens unit 2. A detection unit 13 detects anaperture value of the variable diaphragm 3. A detection unit 14 detectsthe state of entry or exit of the extender lens unit 4.

A calculation circuit 20 of the zoom lens 100 includes an optical systemparameter acquisition unit 21, a depth calculation unit 22, a comparisoncalculation unit 23, a focus operation determination unit 24, a focuscontrol unit 25, a video signal receiving unit 26, and an autofocusevaluation value calculation unit 27.

An image plane variation amount storage unit 31 is connected to thecomparison calculation unit 23 of the calculation circuit 20. The imageplane variation amount storage unit 31 stores data (table data)corresponding to the focal position variation amount Δsk, which isdetermined in relation to the predetermined positional displacementamount ΔFp0 of the focusing lens unit 1.

A distance measurement unit 40 primarily includes a distance measurementoptical system 41, a distance measurement sensor 42, and a phasedifference calculation unit 43. The distance measurement unit 40 isprovided within the zoom lens 100. However, the distance measurementunit 40 can also be provided to the image pickup apparatus 200 instead.

The image pickup apparatus 200, which is provided to the image side ofthe zoom lens 100, includes an image sensor 50. More specifically, theimage sensor 50 is provided at a location within the image pickupapparatus 200 on the optical path of the focusing lens unit 1 of thezoom lens 100.

An output of the image sensor 50 is transmitted to a calculation circuit60, which is connected to the image sensor 50. The calculation circuit60 includes a video signal processing unit 61 and a video signaltransmission unit 62.

FIG. 2 illustrates the principle of distance measurement by the distancemeasurement unit 40. In the example illustrated in FIG. 2, an object Sexists in front of the distance measurement optical system 41.

When the distance to the object S is finite, a phase difference n mayarise between signals incident to a sensor A 42A and a sensor B 42B ofthe distance measurement sensor 42. An object distance L can becalculated (obtained) based on the phase difference n. If the objectdistance L is infinite, the phase difference n is zero.

Let “f” be the focal length of the distance measurement unit 40 and “B”be a baseline length between the sensor A 42A and the sensor B 42B.Then, the object distance L can be expressed by the following expression(1):L=f·B/n   (1).Therefore, the phase difference n and the object distance L have arelationship expressed by the following expression (2):n=1/L   (2).

FIG. 3 illustrates an exemplary method of forming an image by thefocusing lens unit 1, which is provided in the zoom lens 100 at alocation closest to the object side. As a relational expression for aparaxial image forming method, the following expression (3), which isthe Newton's method, can be used:x·x′=−F ²   (3)where “F” denotes the focal length, “x” denotes the distance from thefocus to the object S, and “x′” denotes the distance from the focus tothe image plane. As a result, the relationship between the distance xand the object distance L, if |x|>>F, can be expressed by the followingexpression (4):L≈−x   (4). )

In this case, the position Fp of the focusing lens unit 1, at which thefocusing lens unit 1 is required to be positioned to correct thedistance x′, which is the amount of deviation from the focus, can becalculated by the following expression (5):Fp≈x′  (5).According to the expressions (3) through (5), the following expression(6) can be derived:L=F ² /Fp   (6).The position Fp of the focusing lens unit 1 and the object distance Lhave a relationship expressed by the following expression (7):Fp∝1/L   (7).

FIG. 4 illustrates an exemplary correlation between the phase differencen and the position Fp of the focusing lens unit 1. In the presentexemplary embodiment, the focusing lens unit 1 is provided on the objectside of the variable-magnification lens unit 2. Therefore, the focallength F (FIG. 3) does not vary. Accordingly, the object distance L andthe position FP of the focusing lens unit 1 can be defined on theone-to-one basis independently from variable magnification.

Based on the calculations by the expressions (2) and (7), the phasedifference n and the position Fp of the focusing lens unit 1 areinversely proportional to the object distance L and can be expressed bythe following expression (8):Fp∝n   (8).Referring to FIG. 4, the phase difference n, which is output by thedistance measurement unit 40, and the position Fp of the focusing lensunit 1 are proportional to each other. Accordingly, the phase differencen and the position Fp of the focusing lens unit 1 can be determined onthe one-to-one basis.

After the zoom lens 100 is powered on, the parameters of the opticalsystem for focusing, zooming, the aperture, and the extender, which havebeen detected by the detection units 11 through 14, are transmitted tothe depth calculation unit 22 and the comparison calculation unit 23 viathe optical system parameter acquisition unit 21.

The depth calculation unit 22 calculates a depth of focus ε based oncurrent parameters of the optical system. The depth calculation unit 22transmits the calculated depth of focus ε to the comparison calculationunit 23. As expressed by the following expression (9), the depth offocus ε can be calculated based on the aperture value Fno of thevariable diaphragm 3 and a diameter of a permissible circle of confusionδ. More specifically, the diameter of a permissible circle of confusioncan be appropriately defined as a dimension twice as large as the pitchof a pixel of the image sensor or as a dimension having a range from thedimension equivalent to the pixel pitch to a dimension three times aslarge as the pixel pitch.ε=Fno·δ  (9).

The image plane variation amount storage unit 31 stores datacorresponding to the focal position variation amount Δsk for thepredetermined displacement amount ΔFp0 of the focusing lens unit 1illustrated in FIG. 5 as table data. The table data stored by the imageplane variation amount storage unit 31 includes data on two axes, i.e.,the position Fp of the focusing lens unit 1 and the variablemagnification state Zp. The variable magnification state Zp can includethe position of the variable-magnification lens unit 2 only.Alternatively, the variable magnification state Zp can include theposition of the variable-magnification lens unit 2 and the position ofthe extender lens unit 4.

The comparison calculation unit 23 reads the focal position variationamount ×sk according to the position Fp of the focusing lens unit 1 andthe variable magnification state Zp from the image plane variationamount storage unit 31.

If the table data stored by the image plane variation amount storageunit 31 does not include any value equivalent to the position Fp of thefocusing lens unit 1 or the variable magnification state Zp, thecomparison calculation unit 23 can read the focal position variationamount Δsk of a closest focal position. However, the present exemplaryembodiment is not limited to this. More specifically, alternatively, thevalues in the table stored by the image plane variation amount storageunit 31 can be interpolated by linear approximation to increase theaccuracy of the values.

If it is detected that the extender lens unit 4 has been inserted, avalue acquired by multiplying the focal position variation amount Δsk,which is stored by the image plane variation amount storage unit 31, bya square of the magnification of the extender lens unit 4 is used.However, the present exemplary embodiment is not limited to this. Morespecifically, the same effect can be achieved by the followingconfiguration. More specifically, alternatively, the image planevariation amount storage unit 31 can separately store table data for theextender lens unit 4. In this case, the extender lens unit 4 switchesthe types of the table data according to whether the extender lens unit4 has been inserted.

The phase difference calculation unit 43 of the distance measurementunit 40 calculates the phase difference based on the informationtransmitted from the distance measurement sensor 42. The calculatedphase difference is transmitted to the comparison calculation unit 23.The comparison calculation unit 23 calculates a predetermined variationamount ΔFp of the focusing lens unit 1 corresponding to the receivedphase difference.

The predetermined variation amount ΔFp of the focusing lens unit 1, thepredetermined positional displacement amount ΔFp0, the focal positionvariation amount Δsk, and the depth of focus ε, which are calculated inthe above-described manner, are transmitted to the focus operationdetermination unit 24. The focus operation determination unit 24executes an operation by the following expressions (10) through (12)based on the received values:|ΔFp·Δsk|−ε≦0   (10)|Δsk|−□>0   (11)ΔFp0−|ΔFp|>0   (12).

If the condition expressed by the expression (10) is satisfied, it isnot necessary to execute a focusing operation. Accordingly, in thiscase, no signal is transmitted to components subsequent to the focusoperation determination unit 24.

If the condition expressed by the expression (11) or (and) the conditionexpressed by the expression (12) is (are) not satisfied, the externallight autofocusing is executed by using a first autofocusing unit. Inthis case, the focus operation determination unit 24 transmits a signalto the focus control unit 25 to drive the focusing lens unit 1 by anamount equivalent to the predetermined variation amount ΔFp of thefocusing lens unit 1.

The focus control unit 25 converts the drive amount into a rotationalangle and transmits the rotational angle that is equivalent to anecessary displacement amount to the focus motor 5. The focus motor 5rotationally drives the focusing lens unit 1.

If the conditions expressed by the expressions (11) and (12) aresimultaneously satisfied, the contrast autofocusing is executed by usinga second autofocusing unit. In this case, a video signal input to theimage sensor 50 of the image pickup apparatus 200 is transmitted to thevideo signal processing unit 61. The video signal receiving unit 26 ofthe zoom lens 100 receives the video signal via the video signaltransmission unit 62. In addition, the autofocus evaluation valuecalculation unit 27 extracts the contrast value only. To maximize thecontrast value, the focus operation determination unit 24 instructs thefocus motor 5 to drive the focusing lens unit 1 via the focus controlunit 25.

In the present exemplary embodiment, the autofocus evaluation valuecalculation unit 27 is provided inside the zoom lens 100. However, thepresent exemplary embodiment is not limited to this. More specifically,the same effect can also be achieved if the autofocus evaluation valuecalculation unit 27 is provided to the image pickup apparatus 200.

FIG. 6 is a flow chart illustrating an exemplary flow of an autofocusingoperation executed by the image pickup apparatus according to thepresent exemplary embodiment having the zoom lens 100 illustrated inFIG. 1.

Referring to FIG. 6, instep S10, the zoom lens 100 is powered on andinitialized. In step S20, simultaneously with the end of theinitialization, the optical system parameter acquisition unit 21acquires optical parameters, such as focusing parameters, zoomingparameters, aperture parameters, and extender parameters, from thedetection units 11 through 14.

In step S30, the optical system parameter acquisition unit 21 transmitsthe acquired optical system parameters to the depth calculation unit 22.The depth calculation unit 22 calculates the depth of focus ε based onthe received optical system parameters. The depth calculation unit 22transmits the calculated depth of focus ε to the comparison calculationunit 23.

On the other hand, in step S40, the phase difference n, which has beenacquired by the distance measurement unit 40, is transmitted to thecomparison calculation unit 23. The comparison calculation unit 23calculates the predetermined variation amount ΔFp of the focusing lensunit 1. Then, the comparison calculation unit 23 reads the focalposition variation amount Δsk corresponding to the position Fp of thefocusing lens unit 1 and the variable magnification state Zp from thetable data stored by the image plane variation amount storage unit 31(FIG. 5). The comparison calculation unit 23 then transmits the readfocal position variation amount Δsk to the focus operation determinationunit 24.

In step S50, the focus operation determination unit 24 executes anoperation by using the expression (10) based on the predeterminedvariation amount ΔFp, the focal position variation amount Δsk, and thedepth of focus ε. If the condition expressed by the expression (10) issatisfied (YES in step S50), then the focus operation determination unit24 determines that the focusing operation is not to be executed. In thiscase, the processing returns to step S20.

On the other hand, if the condition in the expression (10) is notsatisfied (NO in step S50), then the processing advances to step S60. Instep S60, the focus operation determination unit 24 executes theoperation based on the expression (11) by using the focal positionvariation amount Δsk and the depth of focus ε.

If the condition in the expression (11) is not satisfied (NO in stepS60), then the processing advances to step S80. In step S80, the focusoperation determination unit 24 instructs the focus motor 5 to drive thefocusing lens unit 1, via the focus control unit 25, by the amountequivalent to the predetermined variation amount ΔFp. In addition, theexternal light autofocusing is executed by using the first autofocusingunit.

On the other hand, if the condition expressed by the expression (11) issatisfied (YES in step S60), then the processing advances to step S70.In step S70, the focus operation determination unit 24 executes theoperation based on the expression (12) by using the positionaldisplacement amount ΔFp0 and the predetermined variation amount ΔFp.

If the condition expressed by the expression (12) is not satisfied (NOin step S70), then the processing advances to step S80. On the otherhand, if the condition expressed by the expression (12) is satisfied(YES in step S70), then the processing advances to step S90. In stepS90, the contrast autofocusing is executed by using the secondautofocusing unit.

More specifically, in step S90, the video signal receiving unit 26 ofthe zoom lens 100 receives a video signal input to the image sensor 50of the image pickup apparatus 200 via the video signal processing unit61.

In step S100, the autofocus evaluation value calculation unit 27extracts the contrast value only. To maximize the contrast value, thefocus operation determination unit 24 instructs the focus motor 5 todrive the focusing lens unit 1 via the focus control unit 25.

In the present exemplary embodiment, the position Fp of the focusinglens unit 1 corresponding to the depth of focus ε is calculated based onthe table data. However, the present exemplary embodiment is not limitedto this. More specifically, the same effect can be achieved by directlycalculating (obtaining) the depth of focus.

FIG. 7 illustrates an exemplary configuration of a second exemplaryembodiment of the present invention. The exemplary embodimentillustrated in FIG. 7 is different from the first exemplary embodimentillustrated in FIG. 1 in the following points. Features corresponding tonumerals already described in reference to FIG. 1 will not be describedto avoid unnecessary duplication.

More specifically, a standard definition (SD)/high definition (HD)receiving unit 28 is provided to the calculation circuit 20 of the zoomlens 100 in the present exemplary embodiment. In addition, an SD/HDtransmission unit 63, which transmits information about which of SD andHD the image pickup apparatus 200 is compliant with, is provided to theimage pickup apparatus 200.

After the zoom lens 100 is powered on, the parameters of the opticalsystem for focusing, zooming, the aperture, and the extender, which havebeen detected by the detection units 11 through 14, are transmitted tothe optical system parameter acquisition unit 21. The optical systemparameter acquisition unit 21 further transmits the received information(the optical system parameters) to the depth calculation unit 22 and thecomparison calculation unit 23.

On the other hand, after a communication with the image pickup apparatus200 is established, information about the image quality (SD or HD) ofthe image pickup apparatus 200 is transmitted from the SD/HDtransmission unit 63 to the depth calculation unit 22 via the SD/HDreceiving unit 28 of the zoom lens 100.

The depth calculation unit 22 calculates the depth of focus ε based onthe current optical system parameters and the type of the image pickupapparatus 200. Then, the depth calculation unit 22 transmits thecalculated depth of focus ε to the comparison calculation unit 23. Thedepth of focus ε is dependent on the permissible circle of confusion δ.The permissible circle of confusion δ differs according to the type ofthe image pickup apparatus 200. Thereafter, the present exemplaryembodiment executes the same processing as that of the first exemplaryembodiment.

FIG. 8 is a flow chart illustrating an exemplary flow of an autofocusingoperation executed by the image pickup apparatus according to thepresent exemplary embodiment having the zoom lens 100 illustrated inFIG. 7. In the example illustrated in FIG. 8, the processing indicatedwith the same step number as that illustrated in FIG. 6 indicates thesame processing as the corresponding processing illustrated in FIG. 6.

In step S20, the optical system parameter acquisition unit 21 acquiresthe parameters, such as focusing parameters, zooming parameters,aperture parameters, and extender parameters, from the detection units11 through 14. Instep S21, the SD/HD receiving unit 28 of the zoom lens100 receives the information about the type of the image pickupapparatus 200 (SD or HD) from the SD/HD transmission unit 63.

In step S30, the received information about the type of the image pickupapparatus 200 is transmitted to the depth calculation unit 22. The depthcalculation unit 22 calculates the depth of focus ε. Furthermore, thedepth calculation unit 22 transmits the calculated depth of focus ε tothe comparison calculation unit 23. Thereafter, the present exemplaryembodiment executes the same processing as that described above in thefirst exemplary embodiment.

In the present exemplary embodiment, the SD/HD transmission unit 63 isprovided to the image pickup apparatus 200. However, the presentexemplary embodiment is not limited to this. More specifically, the sameeffect can be achieved by employing the following configuration. Morespecifically, in this case, the zoom lens 100 can include a modeswitching unit and the user can switch the mode of the image pickupapparatus 200 (SD or HD) by hand.

FIG. 9 illustrates an exemplary configuration of a third exemplaryembodiment of the present invention. The zoom lens according to thepresent exemplary embodiment is different from the zoom lens accordingto the second exemplary embodiment illustrated in FIG. 7 in thefollowing points. More specifically, in the present exemplaryembodiment, a wobbling lens unit 6, which minutely moves along theoptical axis in very small increments to determine the direction of thefocus, instead of the extender lens unit 4 and the detection unit 14 ofthe optical system according to the second exemplary embodiment. Thewobbling lens unit 6 is driven by a wobbling motor 7.

Furthermore, instead of the depth calculation unit 22, the comparisoncalculation unit 23, and the image plane variation amount storage unit31, which are provided in the zoom lens 100 according to the secondexemplary embodiment (FIG. 7), the zoom lens 100 according to thepresent exemplary embodiment includes a wobbling control unit 29, a nearpoint and far point calculation unit 30, and a focus variation amountstorage unit 32.

The focus variation amount storage unit 32 records the relationshipbetween the predetermined positional displacement amount ΔFp0 and adetection resolution of the distance measurement unit 40. Thedisplacement amount ΔFp0 is set at a minimum displacement amountacquired when the detection resolution of the distance measurement unit40 and the displacement amount of the focusing lens unit 1 are set atthe same pitch. Accordingly, as illustrated in FIG. 5, the pixel value(distance measurement value) of the distance measurement sensor 42 andthe position of the focusing lens unit 1 can be uniquely determined.

Accordingly, in the present exemplary embodiment, in determining theposition of the focusing lens unit 1, it is not required to prepare amemory table storing the focus position according to each focal lengthand object distance as it is in the above-described first and the secondexemplary embodiments. Therefore, the processing speed can be increased.

After the zoom lens 100 is powered on, the parameters of the opticalsystem for focusing, zooming, and an iris, are transmitted to theoptical system parameter acquisition unit 21 from the detection units 11through 13. The optical system parameter acquisition unit 21 transmits afocus position “Obj” to the focus operation determination unit 24. Inaddition, the optical system parameter acquisition unit 21 transmits thefocal length F and an F-number Fno to the near point and far pointcalculation unit 30.

On the other hand, after a communication with the image pickup apparatus200 is established, the SD/HD transmission unit 63 transmits informationabout the type of the image pickup apparatus 200 (SD or HD) to the nearpoint and far point calculation unit 30 via the SD/HD receiving unit 28of the zoom lens 100. Because the permissible circle of confusion δdiffers according to the type of the image pickup apparatus 200, thepermissible circle of confusion δ is appropriately selected according tothe received image pickup apparatus type information.

The phase difference calculation unit 43 of the distance measurementunit 40 calculates the phase difference based on the informationtransmitted from the distance measurement sensor 42. Furthermore, theobject distance L is transmitted to the near point and far pointcalculation unit 30.

The near point and far point calculation unit 30 executes operations byusing the following expressions (13) through (17) to calculate ahyperfocal distance H, a near point distance Sn, a far point distanceSf, a resolution “Det” of the distance measurement unit 40, and a depthof focus (Sf−Sn). The result of the calculation is transmitted to thefocus operation determination unit 24.H=f ²/(δ·Fno)   (13)Sf=H·L/(H−L)   (14)Sn=H·L/(H+L)   (15)Det=2L/(n ²−1)   (16)(Sf−Sn)=2H·L ²/(H2−L ²)   (17)where “n” denotes the phase difference of the distance measurement unit40.

On the other hand the focus operation determination unit 24 calculatesthe predetermined variation amount ΔFp of the focusing lens unit 1corresponding to the received phase difference, based on the informationstored on the focus variation amount storage unit 32. The distances Sfand Sn, the resolution Det, and the depth of focus (Sf−Sn) calculated byusing the expressions (14) through (17) and the focus position Objreceived from the optical system parameter acquisition unit 21 aretransmitted to the focus operation determination unit 24.

The focus operation determination unit 24 executes an operationaccording to the following expressions (18) through (20):Sf−Obj>0 orObj−Sn>0   (18)(Sf−Sn)−Det<0   (19)Sf−Obj<0 orObj−Sn<0   (20).

If the condition expressed by the expression (18) is satisfied, then thefocusing operation is not executed. Accordingly, in this case, no signalis output to components subsequent to the focus operation determinationunit 24. If the condition expressed by the expression (19) or (20) isnot satisfied, an autofocusing operation according to a first autofocus(AF) unit (i.e., external light AF) is executed.

In this case, the focus operation determination unit 24 transmits asignal to the focus control unit 25 to cause the focus control unit 25to drive the focusing lens unit 1 by an amount equivalent to thepredetermined variation amount ΔFp.

The focus control unit 25 converts the drive amount into a rotationalangle and transmits the rotational angle that is equivalent to anecessary displacement amount to the focus motor 5. The focus motor 5rotationally drives the focusing lens unit 1.

If the conditions expressed by the expressions (18) and (19) aresatisfied at the same time, then an AF operation by using a second AFunit (i.e., contrast AF) is executed. In this case, a video signal inputto the image sensor 50 of the image pickup apparatus 200 is transmittedto the video signal processing unit 61. The video signal is furtherreceived by the video signal receiving unit 26 of the zoom lens 100 viathe video signal transmission unit 62. The autofocus evaluation valuecalculation unit 27 extracts the contrast value only.

To determine the direction of movement during focusing, in which thecontrast value becomes large, the focus operation determination unit 24instructs the wobbling motor 7 via the wobbling control unit 29 to causethe wobbling motor 7 to minutely drive the wobbling lens unit 6 in smallincrements along the optical axis.

To maximize the contrast value according to the instruction fordetermining the direction, the focus operation determination unit 24instructs the focus motor 5 via the focus control unit 25 to cause thefocus motor 5 to drive the focusing lens unit 1.

As described above, according to the present exemplary embodiment, whichincludes the wobbling lens unit 6 in addition to the configuration ofthe first and the second exemplary embodiments, the autofocusingoperation can be primarily executed at a high speed. In the presentexemplary embodiment, the autofocus evaluation value calculation unit 27is provided within the zoom lens 100. However, the present exemplaryembodiment is not limited to this. More specifically, the same effectcan be achieved if the autofocus evaluation value calculation unit 27 isprovided to the image pickup apparatus 200.

FIG. 10 is a flow chart illustrating an exemplary flow of an AFoperation executed by the image pickup apparatus 200 having the zoomlens 100 illustrated in FIG. 9. Referring to FIG. 10, in step S10, thezoom lens 100 is powered on and initialized. In step S20, simultaneouslyas the end of the initialization, the optical system parameteracquisition unit 21 acquires the parameters, such as focusingparameters, zooming parameters, and iris parameters, from the detectionunits 11 through 13.

After a communication with the image pickup apparatus 200 isestablished, in step S21, the SD/HD receiving unit 28 of the zoom lens100 receives the information about the type of the image pickupapparatus 200 (SD or HD) from the SD/HD transmission unit 63 . In stepS31, the near point and far point calculation unit 30 acquires theoptical system parameter values and type information about the imagepickup apparatus 200.

In addition, the near point and far point calculation unit 30 acquiresthe object distance L from the distance measurement unit 40. Then, thenear point and far point calculation unit 30 calculates the far pointdistance Sf, the near point distance Sn, the detection accuracy(resolution) Det of the distance measurement unit 40, and the depth offocus (Sf−Sn). The near point and far point calculation unit 30 thentransmits the results of the calculation to the focus operationdetermination unit 24.

In step S40, the focus operation determination unit 24 calculates thepredetermined variation amount ΔFp of the focusing lens unit 1, whichcorresponds to the phase difference received from the distancemeasurement unit 40, based on the information stored on the focusvariation amount storage unit 32. In step S51, the focus operationdetermination unit 24 executes an operation by using the expression (18)based on the distances Sf and Sn and the focus position Obj acquiredfrom the optical system parameter acquisition unit 21.

If the condition expressed by the expression (18) is satisfied (YES instep S51), then the processing returns to step S20 because the focusingoperation is not to be executed. On the other hand, if the conditionexpressed by the expression (18) is not satisfied (NO in step S51), thenthe processing advances to step S61. In step S61, the focus operationdetermination unit 24 executes an operation by using the expression (19)using the resolution Det and depth of focus (Sf−Sn).

If the condition expressed by the expression (19) is not satisfied (NOin step S61), then the processing advances to step S80. In step S80, theAF operation by using the first AF unit (i.e., external light AF) isexecuted. More specifically, in step S80, the focus operationdetermination unit 24 transmits a signal to the focus motor 5 via thefocus control unit 25 to cause the focus motor 5 to drive the focusinglens unit 1 by an amount equivalent to the predetermined variationamount ΔFp.

On the other hand, if the condition expressed by the expression (19) issatisfied (YES in step S61), then the AF operation by using the secondAF unit (i.e., contrast AF) is executed. In step S90, a video signalinput to the image sensor 50 of the image pickup apparatus 200 isreceived by the video signal receiving unit 26 of the zoom lens 100 viathe video signal processing unit 61 and the video signal transmissionunit 62. The autofocus evaluation value calculation unit 27 extracts thecontrast value only.

In step S91, to determine the direction of movement for focusing, inwhich the contrast value becomes large, the focus operationdetermination unit 24 instructs the wobbling motor 7 via the wobblingcontrol unit 29 to cause the wobbling motor 7 to minutely drive thewobbling lens unit 6 in small increments along the optical axis. In stepS100, to maximize the contrast value according to the instruction fordetermining the direction, the focus operation determination unit 24instructs the focus motor 5 via the focus control unit 25 to cause thefocus motor 5 to drive the focusing lens unit 1.

According to the autofocusing zoom lens according to each exemplaryembodiment of the present invention, optimum autofocusing can beexecuted in various environments and cases by executing appropriateautofocusing according to shooting conditions and characteristic of theimage pickup apparatus.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent Application No.2010-081437 filed Mar. 31, 2010, which is hereby incorporated byreference herein in its entirety.

1. An autofocusing zoom lens, which is capable of being detachablymounted on an image pickup apparatus and includes, in order from anobject side to an image side, a focusing lens unit configured to moveduring focusing, a variable-magnification lens unit configured to moveduring variation of magnification, and a variable diaphragm capable ofvarying an aperture diameter, the autofocusing zoom lens comprising: aposition detection unit configured to detect a position of the focusinglens unit; a magnification-varying state detection unit configured todetect a position of the variable-magnification lens unit; and anaperture value detection unit configured to detect an aperture value ofthe variable diaphragm; a distance measurement unit configured tomeasure a distance to an object; a communication unit configured tocommunicate with the image pickup apparatus; a video signal receivingunit configured to receive a video signal from the image pickupapparatus; a first autofocusing unit configured to drive the focusinglens unit based on a result of detection by the distance measurementunit; and a second autofocusing unit configured to drive the focusinglens unit based on the video signal from the image pickup apparatus,wherein a near point distance Sn and a far point distance Sf areobtained based on a focal length F and a diameter of a permissiblecircle of confusion δ, wherein if a current focus position Obj and aresolution Det of the distance measurement unit satisfy the followingfirst condition:Sf−Obj>0 orObj−Sn>0, the focusing lens unit is not driven, wherein if the firstcondition is not satisfied and the following second condition issatisfied:(Sf−Sn)−Det<0 andSf−Obj<0 orObj−Sn<0, the focusing lens unit is driven based on the secondautofocusing unit, and if the second condition is not satisfied, thefocusing lens unit is driven based on the first autofocusing unit. 2.The autofocusing zoom lens according to claim 1, wherein the distancemeasurement unit performs the following operations based on an objectdistance (L) from the autofocusing zoom lens to an object, a phasedifference (n) of the distance measurement unit, and a hyperfocaldistance (H) of the autofocusing zoom lens:Sf=H·L/(H−L)Sn=H·L/(H+L)Det=2L/(n ²−1)(Sf−Sn)=2H·L ²/(H ² −L ²).
 3. The autofocusing zoom lens according toclaim 2, wherein communication with the image pickup apparatus isexecuted with the autofocusing zoom lens mounted on the image pickupapparatus, and wherein the permissible circle of confusion δ is switchedaccording to information received from the image pickup apparatus. 4.The autofocusing zoom lens according to claim 1, further comprising amode switching unit configured to switch a mode of the image pickupapparatus, wherein the permissible circle of confusion δ is switchedaccording to the mode of the image pickup apparatus.
 5. The autofocusingzoom lens according to claim 1, further comprising an extender lensunit, wherein the focal length F is switched according to whether theextender lens unit has been inserted.
 6. A camera apparatus comprising:the autofocusing zoom lens according to claim 1; and an image pickupapparatus located on the image side of the autofocusing zoom lens. 7.The autofocusing zoom lens according to claim 1, further comprising awobbling lens unit configured to determine a direction of focus of thesecond autofocusing unit, at a position on the image side of thevariable-magnification lens unit, separately from the focusing lensunit.